With the continuous development of technology, the current commercial lighting products from the first generation of incandescent lamps; the second generation of fluorescent lamps, halogen lamps; the third generation of high-intensity gas discharge lamps and the current mainstream fourth-generation LEDs (led). The lighting efficiency of lighting fixtures is getting higher and higher, and it has been developing towards energy saving and environmental protection. However, it is undeniable that the development of electric light sources has brought many new problems. In addition to the impact on the environment and energy, the impact of artificial lighting environment on human health cannot be ignored. Nowadays, people not only pay attention to the physical performance effects of lighting, but also pay attention to the photobiosafety of lighting. At present, most of the commercial electric light source lighting products are driven by AC. The influence of the stroboscopic effect of the lamps on human health has become a key problem for various lighting products.
The reading and writing work table lamp is an enhanced lighting for people's daily study, work and computer work. Due to the long time of use, it has become one of the lighting products most in contact with human daily activities. Moreover, the population used also includes a large number of adolescents in puberty. The stroboscopic effect of reading and writing desk lamps is also an important factor in inducing myopia in young people. Therefore, in recent years, there has been a "no stroboscopic" protection. Eye table lamp." Since the 'eye protection table lamp' has not undergone rigorous scientific argumentation and impartial third-party testing, and the method of rotating gyro used to verify stroboscopic on the market is very rough and cannot obtain accurate quantitative results, this kind of 'eye protection table lamp' Calling is unscientific.
To sum up, study the stroboscopic effect of reading and writing desk lamps for deep understanding of the stroboscopic mechanism, reduce the adverse effects of reading and writing table lamp illumination on the human body, and create a lighting environment that is highly environmentally friendly, safe and reliable, and beneficial to people's work and life. It has a very important meaning.
Flashing and strobe
The definition of flicker in the ninth edition of the Illumination Manual published by the North American Institute of Illumination (IESNA) is a rapid change in the intensity of the light source. For lighting products, whether it is the traditional light source or the current LED light, as long as it is driven by AC, it will produce flicker. The characterization of the degree of flicker is mainly based on the frequency of the exchange, the persistence of the light emitted by the source and the observation conditions. Blinking has a significant effect on moving objects in the observation range. Under flashing illumination, objects may appear discrete rather than continuous. This effect is called stroboscopic effect. The level of stroboscopic effect depends on the speed and amplitude of the flicker, as well as the rate at which the object moves and the state of observation.
IESNA's lighting experts have proposed the use of flicker percentage and scintillation index to characterize the stroboscopic characteristics of the illumination. The calculation of the two is shown in Figure 1. 
Figure 1. Percentage of periodic waveform flicker with respect to traditional scintillation metrics = 10096x(AB)/(A+B)
The difference between the two metrics is that the percentage of flicker is only the peak-to-peak ratio; the scintillation index is a good illustration of the difference between the output waveforms, and the mathematical characterization is more accurate, but fewer people know the scintillation index and the illumination It is rare to find research in the literature, in part because the scintillation index requires complex mathematical integrals and accurate acquisition of related waveforms. In view of this, the current common stroboscopic evaluation parameter selection flicker percentage is also called the fluctuation depth. The wave depth is the ratio of the difference between the maximum value and the minimum value in one cycle to the sum of the maximum and minimum values ​​of the light output in the periodic light output waveform, expressed as a percentage.
Regarding flicker and stroboscopic, China has not published relevant standards, and only the requirements of flicker are considered in the CQC voluntary certification technical specification "Technical Specifications for Visual Work Table Lamp Certification". The measurement method of stroboscopic is also controversial internationally. There is no unified and effective quantitative analysis method. The current concept of wave depth has been a big step in the study of stroboscopic. The US IEEE released IEEEPAR1789 "Potential Health Effects of LED Lighting Flashing (Draft)" using the depth of fluctuation to assess the stroboscopic effect.
Strobe light biohazard
The impact of light on human health is a long-term, chronic accumulation process, and developed countries in the world have started relevant research very early. According to different factors such as the flickering frequency of light and the variation range of light intensity, the degree of damage of light to the human body is also different. The results of the current study found that the stroboscopic effect causes adverse physiological responses in the human body including:
(1) Headache and eye fatigue
Dr. Wilkins et al. found that office personnel using high-frequency electronic ballast luminaires to reduce headaches by using 50 Hz magnetic ballasts to reduce headaches by a factor of two according to the National Headache Foundation report |5|: "Many migraine patients Light is very sensitive, such as bright light and flicker, which is more likely to cause migraine. Slow blinking is usually more likely to cause migraine than fast blinking." "Some fluorescent lighting or similar effects from the flicker of a television or movie screen have a similar effect."
(2) Photosensitive epilepsy
Light-sensitive people can develop epilepsy even in short-term exposure under visible light modulation in the range of 3-70HZ, which probably affects 1 in 4000 people aged 5-24 years, usually starting around puberty, and 75% of the population will be sensitive to light throughout their lives.
(3) Vision loss
Veitch and McColl discovered in 1995 that a 100-120 Hz modulated inductive ballast fluorescent lamp system would reduce the average visual acuity of a population compared to high frequency electronic ballasts. This often happens in paper reading and text reading on computer screens.
(4) Distraction of attention
The surroundings of the human eye are more sensitive to strobe, such as strobe lights or rapid modulation of the taillights that attract drivers to stare at them. Removing your eyes in advance may be dangerous for drivers or people and things driving on the road. The stroboscopic light source combined with the running machine produces an opening and closing effect, and the damage to the person can result in significantly different movement and stopping speeds. This hazard was identified in the industry ten years ago.
(5) Autism
Children with autism are particularly sensitive to changes in the environment, and stroboscopic lighting increases the recurrence of this behavior. The proportion of children with autism in the United States is about 1/110.
When the human body is exposed to the stroboscopic lighting environment, the conditions that are prone to adverse reactions are: long contact time, large area of ​​the retina receiving stimulation, center of field of view, high brightness of the flash, high contrast with ambient brightness, and deep flash color. red.
The relationship between the fluctuation depth of the stroboscopic frequency and the frequency is shown in Fig. 2. The unaffected area in Fig. 2 is indicated by green, and the low risk area is indicated by orange. The upper limit of the low-risk area is the fluctuation depth line, which is less than 0.08 times the flicker frequency, which is equivalent to 2.5 times the unaffected edge.
Test results and analysis
In order to investigate the stroboscopic characteristics of the reading and writing work table lamps, the strobe test was performed by selecting the reading and writing table lamps of different manufacturers and different light sources. The sample is preheated first during the test, and the light output waveform is obtained after the test is stabilized. The equipment required for the test system used mainly includes Tek~onixTDS2024B digital oscilloscope, Thorlabs photosensitive device and light-shielding box (or darkroom). If detecting small-signal illumination products, a transimpedance amplifier is also needed. The specific test data is shown in Table 1.
For domestic conventional lamps, the light output frequency of the lamp with a fundamental frequency of 50 Hz is generally 100 Hz. It can be seen from the test results in Table 1. The light output frequency of the conventional light source is 100 Hz, but in order to reduce the stroboscopic effect of the LED table lamp, Many LED desk lamps use a variety of circuit rectification methods to change the frequency and waveform of the output light. For example, for LED table lamps in the range of 100 to 120 Hz, the rectification method used includes: full-wave rectification of series LED lamps; direct driving of two parallel LED strings through reverse electrode connection; simple adjustment of pulse width modulation circuit; The number correction circuit 110]~mFig. 2 shows that when the frequency of the light exceeds 3125 Hz, it can be considered that the light has no influence on the health of the human body, and the evaluation can be exempted; when the optical output frequency is <9 Hz, the limit of the fluctuation depth The value is 0.288%; however, when the frequency is between 9 and 3125 Hz, the corresponding fluctuation depth limit is calculated according to the specific frequency. It can be found from Table 1 that the fluctuation depth of the LED reading and writing work table lamp is easier to meet the stroboscopic non-hazard limit, and more qualified (the measured data is bold and non-hazardous, and the standard number is low risk). The marked italic number is unsatisfactory for stroboscopic), probably due to the LED's advantage of flexible and variable drive. Of course, it is necessary to determine whether the LED table lamp has better stroboscopic effect than the lamp of the conventional light source, and it is necessary to obtain more test data for verification in the future.
Figure 3 shows the light output waveform of the reading and writing work table lamp. In the case where the optical output frequency is 100 Hz, the a wave depth exceeds the low risk limit, and b is the strobe pass. It can be seen from the waveform that the strobe of the LED reading and writing work table lamp meets the non-hazard requirement, and one of the solutions changes the peak ratio of the light output waveform by rectifying and filtering the LED driving.
Another method of reducing stroboscopic light can rectify the light output frequency of the LED desk lamp to 50 Hz. It can be found from Table 1 that for an LED read/write work table lamp with an output frequency of 50 Hz, a fluctuation depth value of 5/6 is non-hazardous. Class 4, Figure 4 shows the light output waveform with an output frequency of 50 Hz. This important finding can be found in the IESNA ninth edition of the lighting manual: the human body's eyeball receives the adaptive brightness of the light or in the case of large retinal illumination, the critical flicker frequency is below 60Hz, as shown in the figure 5 is shown. In the future research to reduce the stroboscopic effect of LED reading and writing desk lamps, the frequency of the output light can be greatly increased, or the peak ratio can be changed on the basis of some few 50 Hz, and the fluctuation depth of the light wave cannot exceed the non-hazardous limit. At the very least, it is lower than the limit of the low risk category.
Summary and outlook
This paper studies the stroboscopic characteristics by introducing the concept of stroboscopic light, photobiohazard and strobe detection of reading and writing desk lamps. Based on the analysis of the stroboscopic test results, the effects of waveform and frequency on the fluctuation depth are deeply understood, and the corresponding solution to improve the stroboscopic effect is proposed: the light output waveform of the reading and writing table lamp is changed by rectification and filtering; The frequency of the light, or the peak ratio is changed when the optical frequency is set to 50 Hz. In order to make the reading and writing work table lamp meet the excellent performance, safety and reliability, the illumination and uniformity of the table lamp, the color rendering index and the color temperature are required. The standard of China has already proposed the illumination and uniformity, and the color of the reading and writing table lamp The index (Ra)>80, and R9>0, the color temperature of the desk lamp<4000K, avoiding the high color temperature affecting the routine of the teenagers, but there is no regulation on the stroboscopic requirements, only relevant requirements in the CQC technical specifications. The revision of domestic standards has lagged slightly. Considering that the media and consumers have been paying close attention to the problem of reading and writing desk lamps, it is recommended to improve standards as soon as possible, strengthen government supervision, strengthen consumer safety awareness, and provide high quality reading and writing desk lamps for the masses, especially the youth.
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